One method of examining the gastrointestinal tract for the existence of polyps and other clinically relevant features that may provide an indication regarding the potential of cancer is performed by ingesting an imaging capsule that will travel through the entire gastrointestinal (GI) tract and view the patient's situation from inside. In a typical case the trip can take between 24-72 hours, after which the imaging capsule exits in the patient's feces. When using visible light images may be transmitted directly to an external receiver and combined to form a reconstructed image of the patient's colon. However visible light requires the patient to perform extensive preparations of cleaning out the colon to prevent content from obstructing the imaging process.
Alternatively, an imaging capsule that uses radiation can be used to examine the colon without first cleansing it. Typically the patient ingests a contrast agent to enhance the imaging ability of the imaging capsule. Then the patient ingests the imaging capsule to examine the gastrointestinal tract while flowing through the contrast agent. The imaging capsule typically includes a radiation source, for example including a radioisotope that emits X-rays and/or Gamma rays. The radiation is typically collimated to allow it to be controllably directed in a specific direction during the imaging process. The imaging capsule is designed to measure Compton back-scattering and/or X-ray fluorescence and transmits the measurements (e.g. a count rate of photons having specific energies) to an external analysis device, for example a computer or other dedicated instruments.
In a typical implementation a radio-opaque contrast agent is used so that a position with a polyp will have less contrast agent and will measure a larger Compton back-scattering count and reduced X-ray fluorescence count to enhance accuracy of the measurements.
U.S. Pat. No. 9,037,219 to Baum et al. the disclosure of which is incorporated herein by reference, describes a system and method of estimating distances in the colon with an imaging capsule. The resolution of the reconstructed image is dependent on the accuracy of the estimated distances therefore there is a need for alternative and/or improved methods of measuring distances within the colon to enhance the accuracy of the images.